1. CIS460 – NETWORK ANALYSIS AND DESIGN
CHAPTER 10
Selecting Technologies and Devices for Enterprise Networks

2. Introduction
We are going to look at the technologies for remote-access and WAN components of an enterprise network design
We will talk about physical and data link layer protocols and enterprise network devices such as remote-access servers, routers and WAN switches
What you select will depend on bandwidth and quality of service requirements, network topology, business requirements and constraints and technical goals

3. Remote Access Technologies
Have become a more important ingredient of many network designs
It is important to recognize the location and number of full and part time telecommuters and the extent that mobile users need to access the network
How often and amount of time on the network will drive what you give them

4. Point-to-Point Protocol
Standard data-link-layer protocol for transporting various network-layer protocols across serial, point-to-point links
Can be used for a single user or a group
can be used with ISDN, analog lines, digital leased line, and other WAN technologies

5. Point-to-Point Protocol (Cont’d)
Provides following services: Network-layer protocol multiplexing, link configuration, link quality testing, link-option negotiation, authentication, header compression and error detection
Four functional layers:
Physical layer
encapsulation of network-layer datagrams
Link Control Protocol
Network Control Protocols

6. Multilink PPP and Multichassis Multilink PPP
Adds support for channel aggregation to PPP which can be used for load-balancing and providing extra bandwidth
MPPP ensures packets arrive in order
Multichassis is a Cisco enhancement to MPPP that allows channel aggregation across multi-remote-access servers at a central site

7. Multilink PPP and Multichassis Multilink PPP (Cont’d)
Multichassis MPPP allows multiple access servers to be grouped into a single stack group
Uses Stack Group Bidding Protocol (SGBP) to elect a server to handle aggregation for an application
SGBP can be weighted so that CPU intensive process are offloaded to routers designated as offload servers

8. Password Authentication Protocol and Challenge Handshake Authentication Protocol
Supports both PAP and CHAP authentication
CHAP is more secure than PAP. PAP can be used if remote station does not support CHAP
CHAP is superior. PAP sends password in plain text. An intruder can use a protocol analyzer to capture and use it
CHAP uses a connect, challenge, hashed response and accept/deny reply

9. Integrated Services Digital Network
PPP is often used with ISDN since it provides data encapsulation, link integrity and authentication for ISDN
Cost effective solution for high transmission speed and quick connection requirements
Charge is a basic monthly fee and a usage time charge
MPPP can be used to aggregate ISDN channels

10. ISDN Components Terminal equipment type 1 (TE1)(compliant)
Non-ISDN terminal equipment Type 2 (TE2) (non compliant)
NT1 devices (physical-layer & connect user)
NT2 devices (Layer 2 and 3 protocols)
Reference point interfaces

11. Cable Modem Remote Access
Another option that uses coax cable used for cable TV
Much faster than analog and usually faster than ISDN
some cable-network service providers offer hybrid fiber/coax (HFC) systems that connect CATV networks to the service-providers high-speed fiber-optic network

12. Challenges Associated with Cable Modem Systems
It’s a new technology and there are many standards that do not interoperate with each other
the CATV infrastructure is designed for TV signals in one direction
Usually more bandwidth is offered downstream than upstream
Number of users on system

13. Digital Subscriber Line Remote Access
Growing in popularity with home users
Have to use a DSL modem or other device
DSL uses sophisticated modulation schemes to offer much higher speeds than ISDN, 32Mbps for downstream traffic and 15Kbps to 1.5 Mbps for upstream
Comes in different flavors (ADSL, HDSL, VDSL, SDSL, RADSL, IDSL, and CDSL)

14. Asymmetric Digital Subscriber Line
Has three channels
high-speed downstream from 1.5 to 9 Mbps
medium speed duplex from 16 Kbps to 640 Kbps
POTS 64 Kbps channel for voice

15. High-Bit-Rate Digital Subscriber Line
Provides same upstream and downstream
1.544 over 2 wire pair or Mbps over 3 wire pairs
Has a 12,000 to 15,000 operating distance which is shorter than ADSL’s 18,000 feet
Telco can install repeaters for a price

16. Selecting Devices for Remote Users
Users using for less than 2 hours a day can use an analog modem
Before selecting a modem read reviews for reliability, interoperability with other brands of modems, interoperability with typical services, speed and throughput, latency, ease of setup, support for advanced features and cost

17. Selecting Devices for Remote Users (Cont’d)
Faster access requires cable modems, DSL or a small router that has an ISDN or other type of WAN port
for a router look at: protocol support, support for a remote user or remote LAN, channel aggregation, ease of configuration, security, reliability, interoperability and cost

18. Selecting Devices for the Central Site
Generally includes remote access servers. Five types of services
Remote node services- various devices
Terminal services - Telnet, rlongin X.25, etc
Protocol translation services - access hosts
Asynchronous routing services - layer 3 routing functionality
Dialout services - share access server modems

19. Selecting Devices for the Central Site (Cont’d)
Additional criteria
number of ports and type
support for services
configuration flexibility and modularity
support for network address translation (NAT) or port address translation (PAT) for hosts on remote networks, Dynamic Host Configuration Protocol and multimedia features and protocols

20. WAN Technologies Variety of common and established WAN technologies
Newer technologies are growing such as Wireless WAN
Low-orbit satellite, cellular and radio-frequency wireless will probably become popular option of voice, pager and data services

21. Systems for Provisioning WAN Bandwidth
Must select correct bandwidth required.Varies depending on location. Europe uses 30 B-channels and 1 d-channel for admin purposes, the U.S. uses 24 b-channels and 1 d-channel for admin purposes
the number of digital streams multiplexed together determine network speed

22. Leased Lines
A dedicated circuit that a customer leases from a carrier for a predetermined amount to time usually for months or years
line is dedicated to that customer
Mature and are proven technology
Dedicated to a single customer

23. Synchronous Optical Network
Physical layer specification for high-speed synchronous transmission of packets or cells over fiber-optic cabling
can be ATM or packet-based networks
provides more sophisticated multiplexing and demultiplexing of individual signals
4 layer protocol stack - photonic layer, section layer, line layer and path layer
Usually connected in a ring topology

24. Switched Multimegabit Data Service
SMDS is a physical and data link layer WAN technology alternative to leased lines which runs on fiber or copper media
usually positioned as a high-speed, low-latency, cost effective solution for connecting LANs and MANs over a cell relay WAN
can have just one physical connection to the service provider’s network

25. Frame Relay
High-performance WAN protocol that operates at the physical and data-link layers of OSI
offers a cost-effective method for connecting remote sites typically at speeds from 64Kbps to Mbps
it is efficient, flexible and has low latency

26. Frame Relay Hub-and-Spoke Topologies and Subinterfaces
Frame relay is often designed in hub and spoke topology
A central site router can have many logical connections to remote sites with only one physical connection to the WAN
One problem is that split horizon can limit routing. Distance vector routing protocols do not repeat information out the interface it was received on

27. Frame Relay Hub-and-Spoke Topologies and Subinterfaces (Cont’d)
A solution to split-horizon is to use a full-mesh design with physical circuits between each site
use subinterface which is a logical interface that is associated with a physical interface. The router then applies the split horizon rule based on logical interfaces instead of physical ones
Downside is that router configurations are more complex

28. Frame Relay Congestion Control Mechanisms
A frame relay device has the ability to transmit data at its physical access rate for extended periods of time
Includes congestion control mechanisms to ensure fair bandwidth allocation and feedback mechanisms
Forward-explicit congestion notification
Backward-explicit congestion notification

29. Frame Relay Bandwidth Allocation
Most frame relay networks provides some guarantee of band width availability
Committed information rate (CIR) is the guarantee
At or below CIR will accept it
Leaky bucket
some providers offer zero CIR (inexpensive) only make a best effort

30. Frame Relay/ATM Interworking
As ATM gains popularity WANs that use both ATM and Frame Relay technologies are becoming more popular
Frame Relay/ATM Interworking is used to describe the protocols and processes for connecting ATM and Frame Relay WANs
With network interworking 2 or more frame relay networks are connected via an ATM core network
With service interworking an ATM network connects to a Frame Relay network

31. ATM Wide Area Networks Support ver high bandwidth requirements
copper cabling T3 or above
Fiber optic - speed up to Gbps and beyond
Facilitates efficient sharing of bandwidth among applications with various QoS requirements
Save money spent on monthly tariffs for WAN circuits

32. Selecting Devices and Service Providers for an Enterprise WAN Design
An enterprise WAN design is based on high-performance routers and WAN switches

33. Selecting Routers for an Enterprise WAN Design
High throughput, high availability and advanced features to optimize the utilization of expensive WAN circuits
select to support bandwidth requirements, appropriate packets-per-second level and adequate memory and processing power to forward data and handle routing protocols
Also provide advanced features such as advanced switching and queuing techniques, traffic shaping express forwarding

34. Selecting WAN Switches for an Enterprise WAN Design
Multiservice WAN switches that handle ATM, Frame Relay and remote-access technologies are gaining in popularity
support a variety of data types, interfaces and services and optimize bandwidth utilization
Intelligent queue-handling algorithms that take into account the behavior of different types of applications
Reallocate buffers as needed

35. Selecting a WAN Service Provider
Cost of service but may not be the most important
extent of services and technologies offered
geographical areas covered
reliability and performance characteristics of providers internal network
level of security offered
level of technical support

36. Selecting a WAN Service Provider (Cont’d)
Characteristics of provider’s network:
physical routing of network links
redundancy
extend relies on other providers for redundancy
level of over subscription
bandwidth allocation mechanisms for QoS

37. Selecting a WAN Service Provider (Cont’d)
types of switches and optimization features
frequency and typical causes of outages
security methods from intrusion
security methods for privacy
disaster recovery plans

38. Selecting a WAN Service Provider (Cont’d)
Service Level Support Agreements (SLAs)
experience level of installation and support staff
experience with your particular protocols and applications
dedicated single-point of contact
received ISO 9002 certification
How difficult to provision and price new services
Offer a customer training program

39. Summary There are many options of LANs and WANs
No single technology or device is the right answer for all circumstances
The physical design depends on business objectives, technical requirements, traffic characteristics, and traffic flows
The physical design builds on the logical design