ECE 4400:427/527 - Computer Networks Spring 2015 Dr. Nghi Tran Department of Electrical & Computer Engineering Lecture 3: Network Architectures Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 1

Some Discussions Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 2 We know that there are substantial requirements for NETWORK DESIGN General, cost-effective, fair, robust connectivity among large computers/users Should be manageable by humans of varying levels of skills Network designers have developed general blueprints referred to as NETWORK ARCHITECTURES to deal with complexity Guide the design and implementation of networks

Outline Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 3 In this lecture, we introduce some central ideas common to all network architecture Layering Protocols We also consider two most widely referenced architectures: The OSI -7 –layer Internet architecture

Layering Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 4 Communication network is so complex Contain many pieces: hosts, switching devices, channels, etc How we can manage complexity? Using divide and conquer approach: Idea of Layering

Example of Air Travel Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 5 Travelling contain a series of steps

Layering of Air Travel Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 6 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layers: each layer implements a service – via its own internal-layer actions – relying on services provided by layer below

Why Layering? Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 7 Dealing with complex systems: Explicit structure allows identification, relationship of complex system’s pieces Layered reference model for discussion Modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Layering considered harmful?

Layering Abstraction Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 8 Layer: A set of functionalities encapsulated in an object that can be used by other network components Why layering? Think complexity and common services Layers consist of protocols

Protocols Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 9 Protocol defines the interfaces between the layers in the same system and with the layers of peer system Building blocks of a network architecture Each protocol object has two different interfaces – service interface: operations on this protocol – peer-to-peer interface: messages exchanged with peer

Protocols Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 10 Protocols in each layer have Service interface with upper layer/lower layers Peer-to-peer interface with host on same layer

Hierarchical Layer Structure Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 11 Layering implies the use of a layer hierarchy

OSI 7-Layer Model Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 12 The OSI 7-layer Model OSI – Open Systems Interconnection First formal way defined to connect computers One or more protocols implement the functionality assigned to a given layer Acts like a reference model rather than a real- world protocol graph First three layers are implemented in all network nodes

Description of Layer Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 13 Physical Layer – Handles the transmission of raw bits over a communication link Data Link Layer – Collects a stream of bits into a larger aggregate called a frame – Network adaptor along with device driver in OS implement the protocol in this layer – Frames are actually delivered to hosts Network Layer – Handles routing among nodes within a packet-switched network – Unit of data exchanged between nodes in this layer is called a packet The lower three layers are implemented on all network nodes

Description of Layer Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 14 Transport Layer – Implements a process-to-process channel – Unit of data exchanges in this layer is called a message Session Layer – Provides a name space that is used to tie together the potentially different transport streams that are part of a single application, e.g., synchronization Presentation Layer – Concerned about the format of data exchanged between peers, e.g., encryption, compression Application Layer – Standardize common type of exchanges The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers

The Internet Architecture Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 15 Application: supporting network applications FTP, SMTP, HTTP Transport: process data transfer TCP, UDP Network: routing of datagrams from source to destination IP, routing protocols Link: data transfer between neighboring network elements Ethernet, (WiFi), PPP Physical: bits “on the wire” Application Transport Network Link Physical

Internet Architecture vs OSI Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 16 Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions Session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! These services, if needed, must be implemented in application Application Presentation Session Transport Network Link Physical

The Internet: Protocol Encapsulation Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 17 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch message M HtHt M HnHn frame HtHt HnHn HlHl M HtHt HnHn HlHl M HtHt HnHn HlHl M

Protocol Encapsulation: Example Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 18 Memo: Application-layer message Memo needs to placed on an interoffice envelope and A needs to write an address: Envelope: Transport-layer segment, with header is A’s address Envelope headed to sending office mailroom and placed in a postal envelope; suited for public postal service: Datagram Sending to receiving office mailroom: De-encapsulation begins. B will finally get the memo. A in Office 1 sends to B in Office 2 a memo

The Internet: Alternative View Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 19 Ethernet FDDI FTPHTTPTFTP TCP DNS UDP IP Net 1 FTP: File Transfer Protocol HTTP: Hypertext Transport Protocol TFTP: Trivial File Transfer Protocol FDDI: Fiber Distributed Data Interface TCP: Transmission Control Protocol UDP: User Datagram Protocol IP: Internet Protocol

The Internet: Alternative View Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 20 Subnetwork: Involve sublayers Internet Protocol: Support the interconnection of multiple networking technologies into a single, logical internetwork TCP/UDP: Two main protocols of third layer – TCP: provide a reliable byte-stream channel – UDP: provide an unreliable datagram delivery channel – Sometimes called end-to-end protocols Application We will step by step go through those layers/protocols

TCP vs. UDP Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527Computer Networks 21 TCP: most commonly used protocol on the Internet UDP: Important data? For streaming audio and video; UDP packets in Denial of Service (DoS); also implemented in trojan horse viruses etc. Again, we will step by step go through all these Source: Skullbox.net