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Telecommunications Essentials. Chapter 7 Wide Area Networking. WANs. Networks connected over long distances Integrate voice, data, & video Can be circuit or packet switched. DDS Equipment. Digital Data Service Leased lines operate at 56 or 64 kbps (or multiples)
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Telecommunications Essentials Chapter 7 Wide Area Networking
WANs • Networks connected over long distances • Integrate voice, data, & video • Can be circuit or packet switched
DDS Equipment • Digital Data Service • Leased lines operate at 56 or 64 kbps (or multiples) • DDS Hub is a digital circuit switch • DSU/CSU acts as a digital modem
WAN Switching • Circuit Switched • Leased lines • ISDN • Packet Switched • X.25 • Frame Relay • ATM
WAN Equipment • DSU – Controls the flow between the CPE and CSU • CSU – Performs the line conditioning • Mux – Intelligent time division multiplexer • Routers – Forward the packets • Backbones – T1/T3 or SONET paths
Point to Point • Circuit switched • i.e. A head office has links to each subsidiary • No contention • Limited expansion capability
Multipoint • Circuit Switched • A backbone network is shared by all offices • Competition for resources
WAN Example 1 • Enterprise with 4 separate networks
WAN Example 2 • Enterprise backbone network • Requires intelligent multiplexers
Fractional T-1 • Multiple DS-0s can be concatenated • Supports high speed LAN interconnect • Supports video conferencing • 384 kbps required for full motion video • Frame rate is lowered to 10-15 fps on lower speed links
Bandwidth Allocation • Static • Bandwidth is assigned in 64 kbps chunks • Dynamic • Bandwidth can be assigned in any increment
ISDN • Circuit switched • BRI – 2B+D • Lots of different configurations • PRI – 23B+D (30B+D in Europe) • LAN/WAN integration • www.cisco.com
X.25 • First generation packet system • A virtual circuit system • Designed for data over analog networks • Packet size: 128 or 256 bytes • Error checking occurs at every intermediate node • www.cisco.com
X.25 • Advantages • Addressing capabilities • Can be statistically multiplexed • Basic congestion control • Error control • Disadvantages • Queuing delays • Small packet size • No QoS guarantees • Data only
Frame Relay • Second generation packet system • Used by 60,000 enterprises worldwide • Used in burst environments • Supports SVC & PVC services
Frame Relay • Removes the error correcting from X.25 • Digital transmission media is assumed noise free • The packet is dropped if an error is detected • The end-user application requests a retransmission • Can carry voice and video • Can encapsulate any type of data into the frame • Maximum packet size - 4096 bytes • Cannot predict delay/congestion • Frame Relay Forum
Frame Relay • Advantages • Cheaper than leased lines • Runs on multiprotocol networks • Bandwidth efficient • Disadvantages • Variable delay • Assumed high quality digital links
ATM • Designed to handle data, video, etc. • Can support voice • Provides QoS • 80% of Internet backbones use ATM • www.cisco.com
ATM Cell • 5 byte header • 48 byte payload • Connection oriented • All cells follow the same route as defined by the VPI and VCI
AAL Service Classes • AAL 1 => Service Class A (used for streams) • AAL 2 => Service Class B • AAL 3/4 => Service Class C or D • AAL 5 => Service Class C (used for most other packets)
ATM • Advantages • Supports bandwidth on demand • Provides QoS • Scales in speed and network size • Disadvantages • High overhead • High service cost