MOBITEX and Mobile Data Standards

Mobeen Kahn and John Kilpatrick, RAM Mobile Data

One-line summary: Overview of existing standards (there are so many!) for transmitting packetized data over unreliable RF links, with emphasis on MOBITEX, deployed by Ericsson and used by RAM mobile data.

Overview/Main Points

Existing wireline protocols (e.g. TCP) unsuited for wireless use:

tend to be "chatty"
assume predictable delays or congestion losses
extra overhead to support wide application range

Std	Air IF	NW layer	transport	comments
MOBITEX (Ericsson)	ROSI (GMSK), 12.5 KHz chs, CRC/Hamming, selective ARQ	MPAK (512 bytes, 24 bit addr); proprietary	MTP/1, proprietary	MASC interface: reliable data transfer (in-order?); most widely deployed today
ARDIS	Single freq reuse; 4.8 Kb/s (MDC-4800) or 19.2Kb/s (RD-LAP) in 25 KHz ch	?	?	RD-LAP deployment limited. ARDIS is one of only two nationwide providers. Single freq reuse is economical (single switching gateway, many BS's) but limits capacity.
CDPD (Baby Bells, McCaw)	19.2 Kb/s, FEC	Drafted as proprietary; changed to IP/OSI after pressure from software industry	TCP/OSI	pkt-switching overlay for analog cel voice network. Since must operate within regulatory framework of phone companies, CDPD's must be modular, independent, interoperating networks.
AMPS (cel modem)	Modulate data as voice at ~9600 baud; MNP-10, ETC, V.42bis for EC	None	None	Must be able to stop/restart transmission after handoff or fade
Metricom	FHSS, 902-928MHz (ISM) band, routing within radio mesh	proprietary	TCP/IP, AppleTalk via Hayes AT	Up to 100 Kb/s--NOT

Destineer (MTel): 2-way paging over narrowband PCS; 2 separate networks TDD'd onto a single 50 KHz channel. Great use of a narrow slice of the spectrum, at the expense of response time.

Migration Paths/Future:

Gateways between proprietary and open networks
Wireless extensions to AT cmd set (Portable Computer & Comm. Assoc.), already adopted by Metricom, Ericsson, others. Allows existing apps a cheap (but inefficient) migration path to work over wireless.
WinSock interface
Microsoft Network Driver Interfaces Spec (NDIS), Novell Open Data Link Interface (ODI): standardize interfaces between app-layer protocols and MAC's
Oracle client-server model for isolating client from dissimilar wireless devices; used by RAM Mobile Data

Relevance

Overview of various packet-data standards, plea for standardization, overview of migration issues (primarily at the device driver level).

Flaws

Shameless commercial plug for RAM Mobile Data.

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