HIGH SPEED WIDE AREA NETWORKS BYWANJAU

Introduction  WANs – Group of LANs linked together by communication service providers over large geographically dispersed areas.  They make use of the first two OSI layers (i.e. Physical and Data link layers).  Physical layer defines the media to be used for transmission while data link defines various protocols used for encapsulating data.  E.g of data link layer protocols used by WANs include HDLC, PPP.

ISDN  Uses TDM to enable local loop transmit data. TDM enables physical link to be subdivided into several virtual links.  Uses circuit switching during data transmission  Two types of ISDN: BRI and PRI  PRI – Has 30 B channels (30B+D) or 23 (23B+D) in N. America,(64Kbps each) for carrying data and 1 D channel(64Kbps) for Call setup. (Total Bandwidth=2.048Mbps or 1.54Mbps)  ISDN allows transmission of voice, data, video, images etc over a single physical channel using several virtual channels.

ISDN Emerging Technologies: The High-Capacity (H) Channel – Created specifically for high quality full colour video transmission.  Has 3 variants, H0, H11, H12.  H0 - Has capacity of up to 384Kbps each  H11- Has capacity of up to 1.5 Mbps each  H12 – Capacity of up to 2.044Mbps each

Applications  Useful for video and teleconferencing  Used as backup for leased lines during peak time and when leased lines are down Advantages  Has a short call set up time of about 2 sec.  No latency and low jitter Disadvantages  Long distance communication can be very expensive for multiple connections ISDN

LEASED LINES  They are dedicated communication links reserved by carriers for private customers  They are point to point links that have a bit rate capacity varying from as low as 56Kbps to 2.5Gbps.  Used for applications that need to be online 24/7 e.g. mail servers, e-commerce servers etc.

LEASED LINES Line Type Signal Standard Bit Rate 56DS0 56 Kbps 64DS0 64 Kbps T1DS Mbps E1DS Mbps E3DS Mbps OC-1SONET Mbps OC-3SONET Mbps OC-9SONET Mbps OC-36SONET Mbps OC-48SONET Mbps Some varieties of leased lines are shown below:

LEASED LINES Advantages  No latency, No jitters between end points  Availability in different capacities  Constant availability, no call setup required Disadvantages  Costly equipment  Can be costly for long distances  Changes to the line require onsite service by carrier

Synchronous Digital Hierarchy & Synchronous Optical Network  SONET(N. America) & SDH (rest of the world) are WAN stds. defining how data is transmitted over optical carriers  Both have similar structure and frame formats. Synchronous Transfer Signal for Sonet & Synchronous Transfer Module for SDH  Sonet – STS1 frame using OC1 signal(51.84 Mbps) as the base rate  SDH – STM1 frame format using OC3( Mbps) as the base rate

FRAME RELAY  Its is a network standard, operating in the data- link layer. It is based on packet switching technology.  It uses the HDLC protocol to encapsulate data  Has multiple PVCs within a physical link to enable many connections simultaneously.  It doesn’t perform error & flow control. This is done by DTEs at each end of the link.  Suitable for connecting many LANs within one org.  Uses leased lines and sometimes ISDN for communication.

Frame Relay

FRAME RELAY  As with leased lines, speeds are:  T1 lines 1.544Mbps in N. America & Japan  E1 lines 2.048Mbps in the rest of the world  E3 lines Mbps mostly in Europe Advantages  Low latency and jitters  Cost effective for long distances when using short leased lines.

Cable Modem  Coaxial cable may be used to distribute television and data signals. Results in greater bandwidth.  A cable modem is capable of delivering up to 30 to 40 Mbps of data on one cable channel  Subscribers are able to get television and data services simultaneously  The network provides an always on connection. This may bring about security concerns for organisations. Which are solved by the service provider providing VPN services for large orgs.

Digital Subscriber Line  DSL is a technology that uses broadband to transmit data over existing telephone network  Two main types of DSL:  Asymmetric DSL  Symmetric DSL  Multiple DSL subscriber lines are multiplexed into a single, high capacity link by using a DSL Access Multiplexer (DSLAM) at the provider location using TDM.  ADSL has high download rates( 64 Kbps – Mbps ), lower upload rates( 16 Kbps – 64 Kbps ).  SDSL has equal download and upload rates( Mbps – Mbps ).

Asynchronous Transfer Mode  It is high speed WAN technology capable of data transfer rates of above 155 Mbps  It transfers data in small 53 byte cells, which is useful for transmitting traffic that is intolerable of delay such as voice and video.  ATM uses both PVC and SVC but the former is more commonly used Disadvantages  Less efficient than other technologies. Uses 20% more bandwidth than frame relay.  High over head (5 bytes for each 48 bytes of payload)

SMDS  Switched Multi-Megabit Data Service is neither a type of network nor a protocol. It is a service offered by Telephone companies.  SMDS is defined by the IEEE MAN std.  Its protocols operate within the first 3 layers of OSI ref. model. Most functionality in 2 nd layer.  Transmits data in form of 53 byte cells like ATM  It enables a connectionless link between the CPE and other CPEs or LAN to LAN interconnection.  It uses dedicated links such as T1, E1, T3, E3 lines

Reference Guide:   CCNA Curriculum 