gateways
in the lan design module we saw how bridges and routers may be used to segment large enterprise wide lans into interlans. bridges are level 2 devices and may be used when all nodes in the interlan have unambiguous node addresses. when they don't, node addresses must be decoded by a layer 3 device called a router. but when connecting your lan to a packet switching wan protocol conversions will be required at a level higher than 3 including conversion of email format. the device normally used for such connections is a gateway such as the cisco 5000. multiplexing: fdm, tdm, and statistical tdm
- technology to place more than one channel of data into the same physical line
- fdm: cable tv is fdm: many channels of tv coexist in your cable but in different frequency bands
- tdm: channels take turns using entire frequency range of the line
- time slices allotted to channels or devices
- problem with tdm in bursty data transmission: all channels do not simultaneously demand bandwidth
- but empty slices must be sent anyway to maintain channel integrity
- the data packet itself does not know the destination. this information can only be determined by the time slice in which the data have been sent.
- result: low bandwidth usage in bursty data transmission
- solution: stdm
- data packets contain destination information
- fewer time slices than actual devices (statistical average)
- buffer needed to hold temporary overflow
- see the atm primer for more details
sdlc and bit vs byte oriented protocols- sync vs async comm
- the problem is that these were originally designed to send characters only: transparency problem
- non-char bit patterns used as control info
- question: how do use them now to send non character bit patterns?
- binary sync comm = bsc = byte oriented
- bsc is hierarchical. designed for host terminal comm
- uses ack. not suitable for geosync satellite
- two types of frames: user and control
- sync data link comm = sdlc = bit oriented. hdlc also bit oriented
satellite vs fiber backbone for your wanyour lan design assignment
the datacom warehouse advertises a 'preconfigured network' for $6699. you may order their catalog or obtain technical and pricing information by calling 800-328-2261. please call after 2pm pst. the operators that answer this phone are order takers and can provide very limited technical assistance. for additional technical assistance ask for Bryn or for 'technical assistance'. do not identify yourself as a student. your assignment is to design and price a network configuration consisting of two of these datacomm warehouse networks with a single file server. each of these subnets should be 10 mbps ethernet interconnected with an ether switch. the single file server should serve all 8 stations. we also need a gateway to connect to the internet. assume that a t-1 line to the internet is available. the network should contain a master console with network management capabilities. see their model dds1080 for more info. your report should include a diagram showing the network configuration, parts list, cost buildup, and system capabilities. don't forget that you will need cables and connectors. assume that the entire system is geographically located on the same floor of a 24 x 40 office separated into cubicles with movable partitions.
